This invention relates to an apparatus for producing ignition in an internal combustion engine.
Capacitive discharge ignition (CDI) is an ignition arrangement for internal combustion engines in which ignition is produced when a voltage stored in a capacitor is discharged through the primary winding of an ignition coil. In order to prevent misfiring of an engine, such as when the engine is starting or is cold, an ignition arrangement referred to as long-duration capacitive discharge ignition (LCDI) has been developed. An LCDI system employs first and second capacitors. The first capacitor is connected directly to the primary winding of an ignition coil and is used to initiate discharge, while the second capacitor is connected to the primary winding through an induction coil and is used to lengthen discharge. The capacitors are both charged to a desired voltage, and when it is desired to ignite a cylinder of the engine, the capacitors are discharged. The energy released from the first capacitor into the primary winding initiates discharge of a spark plug of the engine, while a portion of the energy released from the second capacitor is stored in the induction coil. When the capacitors have discharged, the energy stored in the induction coil is then released into the primary winding of the ignition coil, thereby significantly lengthening the discharge time of the spark plug. For example, the discharge time of a spark plug on an LCDI system can be increased from about 100 microseconds to about 1.5 milliseconds compared to the discharge time in a CDI system without a second capacitor and an induction coil.
In a conventional LCDI system, the second capacitor for lengthening the discharge time is always charged to the same voltage, regardless of the operating conditions of the engine. However, the amount of lengthening of the discharge required to prevent misfiring will vary with the engine operating conditions. For example, at a steady engine speed, less lengthening of the discharge time is required than when the engine is just starting and the engine rotational speed is unstable. Therefore, in a conventional LCDI system, the second capacitor may be charged to a greater voltage than required, so electrical power consumption is unnecessarily high. As a result, the amount of heat generated and the size of the ignition apparatus in order to cope with the generated heat are large.
Another problem with conventional LCDI systems is that at high engine speeds, there may not be enough time between the firing of consecutive cylinders to charge both capacitors to the voltage necessary to obtain good ignition, and the likelihood of misfiring increases.